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Full text of "Text Book Of Mechanical Engineering"

798

Appendix IT.

to 10,000 amperes at the plate, passing there through copper
terminals \ in, square, kept cool by water circulation. The
current is very gradually applied, and very slowly shut off, by
means of a rheostatic switch.

The value of nickel steel for armour plates is shewn by the
following figures, which prove a saving in weight of 43*8 % for
equivalent resistance, over ordinary steel plates:—

Kind of Plate.
	Relative penetration.
	Relative resistance.

!
		

Soft Steel         .........
	2*20
	'455

Compound Steel and Iron
	'75
	•572

All Steel           .........
	1*64
	'609

Nickel-Harvey  ...
	J 'OO
	I'OOO

1
		

Chrome Steel is obtained by the addition of chromium to
steel having about -4% of carbon, and the resulting metal is
not only extremely hard, but is * self-hardening,5 that is, it only
needs to be cooled in a current of air after forging, to make it
suitable for metal-cutting tools or armour-piercing shells. For the
latter purpose the French Government use—

Carbon.
•4%

while other analyses give

Chromium.

Nickel.

Carbon °/0
	Chromium °/a
	Manganese °/0
	Silicon %
	

•6
	2*2
	not known
	not known
	French.

•63
	1*04
	•°5
	•i5
	American.

%44
	•92
	*°3
	,.
	American.

A 12 in. chrome-steel projectile has pierced a i6-in. armour
plate, while a chilled chrome-steel armour plate has received a